Method and apparatus for controlling multiple engine aircraft

ABSTRACT

Control means and method for steering an aircraft is disclosed. The aircraft includes engines positioned on opposite sides of its longitudinal axis. The method comprises: selecting an aircraft heading; sensing a deviation from said heading; and varying the thrust of at least one engine in response to the sense deviation.

This invention relates to a method and means for improving the efficiency of multiple engine aircraft by the use of differential thrust output between engines.

BACKGROUND OF THE INVENTION

Aircraft with two or more engines positioned on opposite sides of the longitudinal axis of the aircraft have a tendency to turn if the torque generated by such engines is unequal. In practice, a mismatch in torque is unavoidable. Primarily this is due to the fact that at equal power settings similar engines will differ in power by 1-3%. In addition, oppositely positioned engines frequently are slightly misaligned resulting in turning moments on the aircraft.

During flight, a pilot will set equal power for both engines and position the aircraft to fly a predetermined course. Flight control will maintain this course and overcome the unequal torque of the engines by use of a continuous rudder correction. However, such rudder correction results in a degradation of flight efficiency by creating a drag on the aircraft.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a new and improved method and means for improving the flight efficiency of a multiple engine aircraft.

It is another object of the present invention to match the thrust output of oppositely positioned engines on a multiple engine aircraft.

It is a further object of the present invention to provide a new and improved method and means for minimizing rudder angle drag in a multiple engine aircraft.

It is yet another object of the present invention to provide a new and improved method and means of steering an aircraft without the use of a rudder.

SUMMARY OF THE INVENTION

The present invention applies to an aircraft including two engines positioned on opposite sides of the longitudinal axis of the aircraft. One form of the present invention is a method for steering the aircraft comprising the steps of: selecting an aircraft heading; sensing a deviation from that heading; and varying the thrust of at least one engine in response to the sensed deviation.

Another form of the present invention, in which the aircraft includes a rudder for steering control, is a method for improving flight efficiency. The method comprises the steps of: setting a rudder angle in pursuit of a preselected heading; sensing the rudder angle; and varying the thrust of at least one engine in response to rudder angle to reduce the angle and maintain the preselected heading.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one form of the present invention.

FIG. 2 is a block diagram showing an alternative form of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a control diagram for an engine 10 positioned on one side of the longitudinal axis of an aircraft. The diagram shows control means for varying the thrust of engine 10 in response to sensed deviations from a preselected aircraft heading. Such control means comprises means for selecting an aircraft heading shown in block 12. Such means may include an auto-pilot and a control for setting equal power in oppositely positioned engines and monitoring selected coordinates. The selection of an aircraft heading will typically change many times during the course of a flight. However, for any given heading the presently described means for steering the aircraft will apply.

The control means further includes means for sensing a deviation from the heading by sensing means or deviation sensor 14. There are various means by which deviations from the heading may be sensed. In the simplest form, the deviation is the difference between actual and desired heading, and is available from the flight control. According to a more particular form of the invention, shown in FIG. 1, the aircraft includes a rudder for steering control. Normally, the deviation sensor 14 provides a signal 13 to the rudder control and actuator 15 to set a commanded course correction. A feedback rudder angle signal 17 as measured from the centerline of the aircraft is transmitted to deviation sensor 14. When the deviation in heading is small or zero, the aircraft is flying on the desired course. However, a sustained rudder signal 17 under this condition is undesirable and is corrected as will be described.

The control means further includes means 60 for varying the thrust of engine 10 in response to the deviation sensed by sensor 14. Thrust is varied by analog or digital control of the fuel flow to engine 10. For ease of understanding, an analog system is shown in FIG. 1. However, it will occur to those skilled in the art that a digital system equivalent to that described may be employed. Means 60 include a converter 16, an integrator/limiter 26, valve control means 46, and feedback means 24. The function and operation of which wil become clear from the following.

When the deviation in heading is small or zero, the enable logic 19 closes a switch which allows sustained rudder signal 17 to be transmitted to a converter 16. Converter 16 scales the signal 17 to a desired engine thrust change and generates an error signal 22 as input to on/off switch 20 and thence to summation means or adder 18. Feedback means 24 are provided for modifying error signal 22 in response to a fan speed signal 25. A modified error signal 62 is generated by adder 18 as input to integrator/limiter 26. When the aircraft course heading is correct and the rudder angle is zero, both the rudder position signal 17 and the output error signal 62 of adder 18 will be zero. The on/off switch 20 is provided in the control and governs when the engine steering control will be operative. For example, there may be times during flight when it is not desired to have automatic control for varying engine thrust. In such case, switch 20 will be off. It will be clear that switch 20 may be positioned at other locations in the control. Switch 20 also includes a means of setting error signal 22 to zero when in the off position.

The error signal 62 will be entered into integrator/limiter 26. Integrator/limiter 26 sums over time the error signal 62 received from adder 18 and generates an output in the form of an engine speed signal 28 in response thereto. The signal 28 will be restricted within predetermined limits to prevent an excessively large signal 28 from being generated. Signal 28 may be entered directly into valve control means 46 for controlling fuel flow 52 in response to speed signal 28. Valve control means 26 includes a power amplifier 30 for driving an electrohydraulic servo valve or torque motor 32 and fuel control valve 34. According to an alternative form of the invention, signal 22 may be summed with other fan speed (N₁) control signals 36. In this manner, a single power amplifier 30, motor 32, and valve 34 may be used by several control functions for each engine 10.

To control fan speed N₁, negative feedback of such speed will be entered into summer 18. In this manner, fan speed N₁ will approach the sum of other N₁ signals 36 and error signal 22. The present invention contemplates monitoring fan speed N₁ as an indicator of engine thrust. Other engine parameters, such as engine or fan pressure ratio, may similarly be monitored and are within the scope of the present invention.

According to one form of the present invention, an aircraft may be steered by the control means disclosed. This would apply to aircraft with no means of steering other than by differential engine thrust as well as aircraft with movable control services such as a rudder but where such control surfaces are locked in a fixed position. In operation, deviation sensor 14 will continuously monitor heading errors which will be converted, as described above, to a signal for varying the thrust of engine 10 in response to the sensed deviation.

The invention applies equally to an aircraft with movable control surfaces such as a rudder for steering control. In such case, rudder position will be continuously monitored to minimize its angle while maintaining a predetermined heading. Rudder angle is measured from the longitudinal centerline of the aircraft so that an angle of zero corresponds to an alignment of the rudder with such centerline. Deviations from a zero angle result in aircraft drag.

In operation, the control is designed to improve flight efficiency. The method comprises the steps of setting a rudder angle in pursuit of a preselected heading, sensing the rudder angle, and varying the thrust of at least one engine in response to rudder angle to reduce the angle and maintain the preselected heading. The rudder angle may be sensed and the thrust varied continuously so as to minimize the angle.

The method may further comprise the step of selecting a thrust for each engine prior to or after selecting an aircraft heading. In normal operation, the pilot will set each engine for equal thrust. However, slight variations in thrust between the several engines as well as sight misalignments of the engines will create a turning moment about the longitudinal axis of the aircraft. Typically, the pilot will preselect a heading and the flight control will automatically set rudder angle in pursuit of that preselected heading. The rudder angle will create a drag on the aircraft which reduces flight efficiency. By sensing the rudder angle and varying the thrust of at least one engine in response to rudder angle, the angle, and consequently drag, will be reduced.

FIG. 2 shows an alternative form of the present invention wherein the thrust of two engines positioned on opposite sides of the longitudinal axis of an aircraft are simultaneously controlled. Each engine 10 and 10a will be controlled in a manner similar to that shown in FIG. 1. However, an inverter 40 will be inserted in the control for engine 10a to change the sign of signal 22a coming from converter 16. In this manner, engine 10a will be reduced in power while engine 10 is being increased in power or vice versa as required by the signal received from deviation sensor 14.

It will be clear to those skilled in the art that the present invention is not limited to the specific embodiments described and illustrated herein. Nor, is it limited by any particular network for controlling engine thrust. Rather, it applies equally to any automatic control system which is capable of sensing a deviation from a preselected heading and varying the thrust of at least one engine in respone to the sensed deviation.

Numerous modifications, variations, and full and partial equivalents can now be undertaken without departing from the invention as limited only by the spirit and scope of the appended claims.

What is desired to be secured by Letters Patent of the United States is the following. 

I claim:
 1. In an aircraft including two engines positioned on opposite sides of the longitudinal axis of said aircraft, a sensing control mechanism, a thrust control mechanism, and a rudder for steering control, a method for improving flight efficiency comprising the steps of:a. setting a rudder angle in pursuit of a preselected heading; b. sensing said rudder angle using said sensing control mechanism; and c. varying the thrust of at least one engine using said thrust control mechanism in automatic response to rudder angle to reduce said angle and maintain said preselected heading.
 2. A method, as recited in claim 1, further comprising the step:d. repeating steps b and c to continuously minimize said angle.
 3. In an aircraft including two engines positioned on opposite sides of the longitudinal axis of said aircraft, a thrust control mechanism, and a rudder for steering control, a method for improving flight efficiency comprising the steps of:a. selecting a thrust for each engine; b. setting a rudder angle in pursuit of a preselected heading; c. varying the thrust of at least one engine using said thrust control mechanism in automatic response to rudder angle to reduce said angle; and d. repeating steps b and c to continuously minimize said angle.
 4. In an aircraft including two engines positioned on opposite sides of the longitudinal axis of said aircraft, a sensing control mechanism, and a thrust control mechanism, a method for steering said aircraft comprising the steps of:a. selecting an aircraft heading; b. sensing a deviation from said heading using said sensing control mechanism; c. producing a signal indicating a desired thrust in response to the deviation sensing step; d. monitoring a signal indicating engine thrust; and e. controlling the fuel flow to at least one of the engines in response to the desired thrust signal and the signal indicating engine thrust.
 5. The method of claim 4, in which the controlling step comprises the step of:modifying the desired thrust signal in response to the signal indicating engine thrust.
 6. The method of claim 5, in which the controlling step further comprises the step of:integrating the modified desired thrust signal.
 7. The method of claim 5, in which the controlling step further comprises the step of:integrating and limiting the modified desired thrust signal.
 8. In an aircraft including two engines positioned on opposite sides of the longitudinal axis of said aircraft, a sensing control mechanism, and a thrust control mechanism, a method for improving flight efficiency comprising the steps of:a. selecting a thrust for each engine; b. selecting an aircraft heading; c. sensing a deviation from said heading using said sensing control mechanism; d. producing a signal indicating a desired thrust change in response to the deviation sensing step; e. monitoring a signal indicating engine thrust; f. controlling the fuel flow to at least one of the engines in responses to the desired thrust change signal and the signal indicating engine thrust; and g. repeating steps c through f to continuously minimize said deviation.
 9. The method of claim 8, in which the controlling step comrpises the step of:modifying the desired thrust change signal in response to the signal indicating engine thrust.
 10. The method of claim 9, in which the controlling step further comprises the step of:integrating the modified desired thrust change signal.
 11. The method of claim 9, in which the controlling step further comprises the step of:integrating and limiting the modified desired thrust change signal.
 12. The method of claim 1, in which the thrust varying step comprises the steps of:producing a signal indicating a desired thrust in response to the deviation sensing step; monitoring a signal indicating engine thrust; and controlling the fuel flow to at least one of the engines in response to the desired thrust signal and the signal indicating engine thrust.
 13. The method of claim 12, in which the controlling step comprises the step of:modifying the desired thrust signal in response to the signal indicating engine thrust.
 14. The method of claim 13, in which the controlling step further comprises the step of:integrating the modified desired thrust signal.
 15. The method of claim 13, in which the controlling step further comprises the step of:integrating and limiting the modified desired thrust signal.
 16. The method of claim 3, in which the thrust varying step comprises the steps of:producing a signal indicating a desired thrust change in response to the deviation sensing step; monitoring a signal indicating engine thrust; and controlling the fuel flow to at least one of the engines in respones to the desired thrust change signal and the signal indicating engine thrust.
 17. The method of claim 16, in which the controlling step comprises the step of:modifying the desired thrust change signal in respone to the signal indicating engine thrust.
 18. The method of claim 17, in which the controlling step further comprises the step of:integrating the modified desired thrust change signal.
 19. The method of claim 17, in which the controlling step further comprises the step of:integrating and limiting the modified desired thrust change signal. 